Engine power tests are conducted in accordance with SAE Standard Engine Power Test Code for diesel engines (SAE J1349 Revised MAR2008). Baseline engine performance and emissions tests are performed using ULSD reference diesel fuel. Engine performance data for ULSD reference diesel were corrected to the standard atmospheric conditions using the compression ignition engine correction formula according to SAE J 1349-MARCH 2008.

Variables such as air and relative humidity are carefully monitored. Fuel temperature is controlled as outlined in the test procedure. Tests were conducted in a randomized complete block design (RCBD) to prove that the fuel sequence is not significant to the results of the study. Response variables were the following: net brake power (kW), torque (N-m), fuel consumption (L/h), NO_x concentrations (ppm), unburned hydrocarbon concentrations (ppm), CO concentrations (ppm), and CO₂ concentrations (%).

The BETA lab is equipped with a NI Labview program that can perform remote-based switching of fuel source. This provides changing of test fuels without turning off the engine. At each fuel change, the fuel filter was replaced and then the engine was warmed at idle speed on the new fuel for 15 minutes to purge remaining previous test fuel from the engine’s fuel system. Then, the engine was operated at full throttle and prepared for the next performance testing. Also, a new set of sintered filters for the exhaust emissions analyzer was installed prior to the next emissions testing.

The important sources of uncertainty in this study are: 1) supply of consistent quality of fuel, 2) proper control over relevant engine parameters (e.g. speed and load), and 3) proper use and calibration of the measurement instruments. To minimize the first source of uncertainty, test fuels were processed in such a way that it will match up ASTM 6751 standard. Fresh batch of biodiesel was used to ensure consistency of the fuel quality in the experiment. Having proper control and use of engine instrumentation and controller equipment minimized uncertainty associated with the second source. Parameters, such as engine speed, fuel flow rate, and load accuracy were matched to within ±5 RPM, ±1% of the reading, and ±0.05% of the rated output, respectively. Finally, uncertainty associated with the third source was minimized through routine calibration of emissions equipment and all other instruments (e.g. pressure transducers, thermocouples, flow rate meters, etc.) prior to start of testing.

In order to understand the effect of the biodiesel on engine combustion efficiency, the brake specific fuel consumptions (BSFC) for the test fuels were measured at peak torque condition. This condition was chosen since it is the point of minimum air/fuel ratio and maximum smoke [7] . Results were compared to those of the control fuel using statistical analysis procedures (Analysis of Variance and Fisher’s Least Significant Difference Test).

1) Small engine

The net brake power at different engine speeds and test fuels are presented in Figure 1. At different engine speeds, there is an initial gradually increasing trend in power until a maximum is reached and then it falls rapidly as the engine speed is further increased. Power decreases after a maximum is reached due to increase in friction at higher speeds. The net brake power, as defined by the Society of Automotive Engineers [42] , is a measure of the engine’s horsepower delivered directly to the engine’s crankshaft without the loss in power caused by the accessories such as the gearbox, alternator, differential, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc.

As observed in Figure 1, the corrected peak brake power for REFDIESEL is at 13.5 kW (18.0 hp) at an engine speed of approximately 2940 rpm. Similar results were obtained using B100 SME. The net brake power for B100 PME was only 2% higher than REFDIESEL with 13.7 kW. Other test fuels (i.e. B100 CME and B100 SFME) are 1% lower than REFDIESEL with both fuels obtaining 13.3 kW. This negligible loss in power was also observed by Lin et al. [43] , who observed that the maximum differences in engine power at full load between petroleum diesel and eight kinds of vegetable oil methyl esters is only about 1.49%. They attributed this to the higher viscosity, fuel consumption, oxygen content and combustion rate of biodiesel. Also, Qi et al. [44] reported the same trend and explained that since engines deliver fuel on a volumetric basis, the higher density of biodiesel as compared to diesel implies more fuel is delivered and this compensates for the lower heating value of biodiesel, thus yielding negligible power loss in comparison with petroleum diesel. Others also reported that insignificant changes in engine power can be obtained even when using different feedstocks such as waste palm oil and canola oil methyl esters [45] and soybean, rapeseed and palm oil biodiesels on a 3-cylinder, 4-stroke, 30-kW diesel engine [46] .

2) Large engine

For the 4-cylinder-80-hp John Deere engine, the net brake power at different engine speeds as shown in Figure 2 follows the same trend as with the small engine. The corrected peak net brake power using REFDIESEL was observed to be the highest compared to the biodiesel fuels. Percent differences in peak net brake power were from 0.2% to 2%. Similar explanations as with the small engine can be applied to these observations.

The engine torque at varying engine speed and fuel blends for the large engine were also obtained and shown in Figure 3. The torque is a good indicator of an engine’s ability to do work and is a function of engine speed. Similar to engine power, the torque was gradually increasing at low speed and decreased rapidly after a maximum

value was reached. Torque decreases because the engine is unable to ingest a full charge of air at higher speeds [47] .

Moreover, the peak torque value for REFDIESEL was higher than peak torque values for biodiesel fuels, except for CME, which has similar peak torque value as with REFDIESEL. The highest decrease in peak torque value was observed for CFME, corresponding to a 2.9% decrease from 293.2 N-m at 770.3 rpm for REFDIESEL 284.8 N-m at 825.5 rpm for CFME. The other test fuels have peak torque values that are 1.2% - 1.5% lower than REFDIESEL. The different biodiesel fuels performed similarly with the reference diesel.

1) Small engine

The brake specific fuel consumption (BSFC) is a measure of fuel efficiency within the crankshaft of an internal combustion engine and can be obtained by dividing the rate of fuel consumption of the engine by the net brake power [47] . Figure 4 shows the BSFC in relation to varying engine speed and fuel blends for the Yanmar engine. The BSFC is observed to decrease with an increase in engine speed until it reaches a minimum value and further increases at higher speeds. Greater friction losses at higher speeds contribute to the increase in fuel consumption while at low speed, the longer time per cycle results in higher heat loss, allowing for more fuel consumption.

Using analysis of variance, at peak torque conditions, the BSFC’s for all biodiesel fuels as compared to the

reference fuel has increased significantly, with 14%, 10%, 9%, and 5% increase for SME, CME, PME and SFME, respectively. An increase in BSFC was also observed by Moreno et al. [39] , when they fueled a four- cylinder, turbocharged, indirect injected Isuzu engine with pure sunflower oil biodiesel. The BSFC increased by approximately 12% higher than with pure diesel fuel. Kaplan et al. [48] also observed similar results. The observed increase in fuel consumption when using biodiesel can be attributed to the combined effects of the biodiesel properties such as lower heating value and higher density and viscosity as compared to a regular diesel [38] [49] . The higher density of biodiesel indicates that higher mass is injected for the same volume at the same injection pressure while the lower calorific or heating value indicates that a larger quantity of fuel must be injected into the combustion chamber to produce the same power, thus leading to an increase in the specific fuel consumption [49] .

2) Large engine

Figure 5 shows the BSFC at different engine speeds when running the large John Deere engine with the different biodiesel fuels and reference diesel. Higher BSFC was again obtained for REFDIESEL as compared with the biodiesel fuels. Using analysis of variance, at peak torque conditions, SaffME obtained the highest BSFC with 314.8 g/kW-h, while REFDIESEL obtained the lowest with 248.8 g/kW-h. Similar explanation as with the small engine can be applied in these observations. On the other hand, Fisher’s least significant difference test indicated that there is no strong evidence of differences among SME, SFME and PME test fuels.

Also, it is interesting to note that the large engine had relatively lower BSFC values than the small engine. BSFC values range from 267 - 308 g/kW-h for the small engine while it ranges from 248 - 278 g/kW-h for the large engine. According to Pulkrabek [47] , BSFC generally decreases with engine size, being best (lowest) for very large engines. One reason for this is that large engines have less heat loss due to the higher volume-to-sur- face-area ratio of its combustion chamber. Also, larger engines operate at lower speeds, which reduce friction losses.

Exhaust emissions of the Yanmar 3009D test engine using the different test fuels are shown in Figure 6. In general, all biodiesel fuels under study have higher NO_x concentrations than the reference fuel. The same was observed by many other researchers concerning the NO_x emissions when using biodiesel. A maximum of 15% increase in NO_x emissions for B100 was observed by Nabi et al. [51] at high load condition which was attributed to the 12% oxygen content of the B100 and higher gas temperature in combustion chamber. A greater increase in NO_x emissions (22.1%) was observed by Ozsezen et al. [45] when they employed waste palm oil biodiesel on a 6-cylinder WC, NA, DI diesel engine while canola biodiesel produced NO_x emissions higher than petrodiesel by 6.5%. The increase in NO_x emissions could have been affected by the differences in the fuel properties between diesel and biodiesel. According to Moser et al. [52] , the higher density and viscosity of the biodiesel imply that the differential pressure at the advance piston contained in the distributor pump is slightly increased, which in turn advances injection. Also, the amount of fuel injected per cycle could also be affected by variations in density in the fuel. In addition, the fuel spray properties might also be modified due to increases in the size of the droplets of the fuel, thus affecting burning of the fuel [52] . The increase in NO_x emissions could also be related to the higher oxygen content of biodiesel, as it may provide additional oxygen for NO_x formation [53] .

The CO emissions, on the other hand, decreased as the engine speed increased and were lower for the biodiesel fuels in comparison with the reference diesel. Puhan et al. [54] also observed a decrease of around 30% in CO emissions when they used Mahua oil biodiesel instead of petroleum diesel. Utlu et al. [55] observed a 17.1% decrease when using waste frying oil biodiesel and Wu et al. [56] reports an average of 4% - 16% CO reduction for five biodiesels. The lower CO emissions can be attributed to the higher oxygen content of biodiesel as compared to petroleum diesel, which promotes complete combustion and thus, reduction in CO emissions [57] - [60] .

CO₂ emissions followed the same trend as CO emissions with respect to engine speed but were found to be higher for the biodiesel fuels as compared with the reference diesel. Other researchers also report that the CO₂ emissions increase when an engine is ran on biodiesel due to more efficient combustion [57] [61] - [65] . Nevertheless, others reason out that this can be offset by planting and raising biodiesel crops as supported by life-cycle assessment of CO₂ emissions from biodiesel [65] [66] . About 50% - 80% reduction in CO₂ emissions can be obtained when using biodiesel [67] .

The emissions of THC, on the other hand, seemed to be not affected by the engine speed and were found to be higher for the biodiesel fuels; with comparable for SME, PME and CME test fuels but higher value for SFME. A similar increase in hydrocarbon emissions was observed by Muñoz et al. [50] at high engine speed and load. They explained that hydrocarbon emissions increased since the higher density and viscosity of biodiesel changes the characteristics of the fuel jet, i.e. size of droplets, penetration, etc., liberated by the injector. It also increases the amount of fuel retained in the interior of the injector nozzle, and therefore cannot be incorporated in the combustion chamber immediately, causing an increase in the hydrocarbons without burning.

Lastly, negligible SO₂ concentrations were lower for PME as compared with REFDIESEL, a proof of obtaining lower sulfur emissions when using biodiesel rather than petroleum diesel.

The emissions of the large John-Deere engine using different test fuels are shown in Figure 7. Similar to the small engine emissions, NO_x concentrations tend to decrease as the speed of the engine is increased. Also, REFDIESEL obtained the lowest peak NO_x concentrations with 454 ppm at 1203 rpm. Highest NO_x emissions at peak torque conditions were observed for CME at 38% increase, corresponding to NO_x concentrations of 627 ppm. This increase can be explained by the reasons described earlier for the small engine.

CO₂ concentrations were observed to gradually increase as the speed was increased up to a certain point (2050 rpm) only and then decreased rapidly up to peak power conditions. CO₂ emissions were higher for CME as compared with those of SME and REFDIESEL at the given range of engine speed. At peak torque conditions, CME has around 17.5% higher CO₂ emissions than SME. SME and REFDIESEL have comparable CO₂ emissions while the other biodiesel fuels have slightly higher emissions than REFDIESEL.

CO, THC and SO₂ concentrations, on the other hand, tend to peak as they approach peak power conditions. Similar to the small engine, there was a reduction in CO emissions when using the biodiesel fuels than the reference diesel, which yielded 138 ppm CO emission at peak torque conditions. THC emissions, on the other hand,

were higher by around 33% - 47% for CME, SME and SFME as compared to REFDIESEL, but slightly lower, if not comparable, for CFME, SAFME and PME. Finally, negligible SO₂ emissions were obtained for all test fuels at peak torque conditions.